In existing mobile communication networks, user data is collected via Radio Base Stations of a Radio Access Network (RAN), and then sent via terrestrial transport networks towards nodes of a Core Network. Network components implementing the transport from RAN to Core Network nodes are generally referred to as a Mobile Transport Network (MTN) or Mobile Backhaul Network (MBH). The MTN implements an IP packet transport service (IP TNL) for the RAN, and the main interfaces used to transport user traffic between the RAN and the Core Nodes are implemented with the GPRS Tunnelling Protocol User Plane (GTPv1-U protocol), defined in TS 29.281.
Examples of interfaces implementing the GTPv1-U protocol are set out in TS 29.281 and some of these interfaces are illustrated in FIG. 1, which shows an example LTE Radio and Core Network, taken from 3GPP TS 23.401. Example interfaces include, in 2G networks the Gn and Gp interfaces of the General Packet Radio Service (GPRS), in 3G networks the Iu, Gn and Gp interfaces of the UMTS system, and in 4G and 5G networks the S1-U, X2, S4, S5, S8 and S12 interfaces of the Evolved Packet System (EPS). The S1-U interface is a typical example of interfaces implementing the GTPv1-U protocol. The S1-U interface is illustrated in FIG. 1 between the eNodeBs of the E-UTRAN and the Serving Gateway (SGW) core node. The S1-U interface transports flows for 4G networks and will also in the future transport flows in 5G networks.
FIG. 2 illustrates the protocol stack of the GTPv1-U protocol used to implement the S1-U interface between an eNodeB and the SGW. The GTPv1-U protocol stack multiplexes several user tunnels onto the same S1-U interface. In order to distinguish the tunnels, the GTP protocol defines a Tunnel Endpoint Identifier (TEID) for each user tunnel carrying user IP data. The GTP protocol itself is in turn carried over UDP packets, with common practice being to use a single pair of UDP source and destination ports for a given GTP tunnel in a radio base station. The UDP is in turn carried by IP packets.
User traffic carried over an interface may be of different kinds, including for example data and voice traffic, and may require different treatment as regards Quality of Service (QoS). QoS information contained in a user data packet is generally copied to the DSCP field of the header of the IP packet supporting GTP over UDP, enabling the information to be accessed for the purpose of routing the packet over the GTPv1-U interface. However, 3G, 4G and in the future 5G packets may carry additional QoS information, specific to the Radio Access Technology (RAT), which cannot be mapped to the DSCP field. Examples of such information include Traffic Handling Priority (THP) in 3G and QoS Class Identifier (QCI) in 4G.
The above described GTPv1-U interfaces, including S1-U, are carried by the MTN network, which is normally operated independently of the RAN and Core Network. However, information available to the RAN and Core Network about the traffic flowing over GTPv1-U interfaces may be useful to the MTN in optimising interface performance and traffic throughput. For example, in order to properly comply with QoS requirements for individual traffic flows, the MTN should be provided with QoS information for individual user packets. As discussed above, basic QoS information is copied to the DSCP field of the IP header and is thus relatively easily available to the MTN network. However, RAT specific QoS information, which would ideally also be taken into account by the MTN, cannot be copied to the DSCP field, and is only known to the RAN and Core Network nodes exchanging traffic over the interface.
Traffic flow information could also be useful to the MTN in implementing load balancing. If the traffic flowing over an interface must be split onto different resources in the MTN, for example if Link Aggregation or Equal Cost Multipath is implemented, packets belonging to the same user flow should be kept on the same physical resource path, in order to avoid packet reordering. The information enabling identification of individual user flows is the TEID number assigned to each packet, which specifies which GTP tunnel the packet belongs to. However, this information is contained in a GTP header field of a user data packet, and Deep Packet Inspection (DPI) is therefore required to access the TEID information for a user packet, and to ensure that load balancing does not separate the packets of individual user flows. DPI is a more resource intensive procedure than standard shallow packet inspection, and not all commercial routers providing a MTN network are able to implement it. In addition, if IPsec tunnels are implemented over the interface, DPI is impossible.
It can be seen from the above discussion that there may be situations in which the MTN network does not have sufficient information about the user data packets being transferred over a GTP interface to manage the routing of the packets over the interface in an optimal manner.